The restriction relation page has examples of how to use the "via" member role: osm.wiki/Relation:restriction#Members

Turn restriction relations can restrict going straight through an intersection, and can restrict specific types of vehicle: osm.wiki/Relation:restriction

If the tags on a node in a way only apply to one side or one direction, that can be indicated with a suffix on the key: osm.wiki/Forward_%26_backward,_left_%26_right

Mapping traffic signals at the way intersections is valid: highway=traffic_signals

way/1223146051 is incorrect. Only physically separate roads can be separate ways. Lanes, connectivity, and turn restrictions should use their appropriate relation types.

Please use the changeset description field to describe what you changed and why—for example, "reclassified Stanford Arboretum as a forest instead of a park." More examples here: osm.wiki/Good_changeset_comments

Thanks. The tags were added in changeset/29688748 , so you could ask the author of that change, or go to the VTA, the source they list.

Ah, I didn't know it hasn't passed yet: there's an open proposal for allowing other units in ele= osm.wiki/Proposal:Ele_with_units

The reason it's in feet is because that's what's on the sign, so it directly describes the sign; tagging with on-the-ground information is preferred over external sources.

If it's verifiable and you can't find a better tag, leave it alone, even if it's a unique tag, otherwise you're just deleting good data for no reason. See osm.wiki/Any_tags_you_like

Fixed in changeset/143180287

indoor=room is not allowed outside of a building outline.

I don't think it really makes sense for a room to be outside of a building. What are you trying to describe?

Could you put in the "sources" changeset tag where you're getting the information on these? The pipelines are tagged as being underground, and aren't visible in imagery. Thanks!

Please use the changeset comment field to describe what you changed and why; for example, "added taxiways and grass areas in airports." More examples here: osm.wiki/Good_changeset_comments Also, please save your changes in one area before moving to another, to keep the changeset area small.

…for the roofs that still exist, anyway (I was looking at old imagery)

Standalone roofs can be mapped with building=roof. That would be appropriate here.

The "picnic site" feature preset (tag tourism=picnic_site) is meant for areas with room for multiple groups, not just a single table. For that, a "picnic table" (tag leisure=picnic_table) on a node is enough.

Welcome to OpenStreetMap! Please use the changeset description field to describe what you changed and why; for example, "added the name to a religious building." There are more examples and guidance here: osm.wiki/Good_changeset_comments

Thanks for contributing to OpenStreetMap! In the future, please save your changes in one area before moving on to another; this keeps the changeset to a reasonable size.

man_made=chimney is for large, industrial chimneys, not individual houses: man_made=chimney Private backyards generally shouldn't be micromapped, to protect people's privacy: osm.wiki/Limitations_on_mapping_private_information

The name:etymology:wikipedia and operator:wikipedia you added don't match the name:etymology:wikidata and operator:wikidata that were already there